Captcha and Image-recognition CAPTCHAs
May 20th, 2008 by sherlock Hit :: 523
A CAPTCHA system is a means of automatically generating new challenges which:
- Current software is unable to solve accurately.
- Most humans can solve.
- Does not rely on the type of CAPTCHA being new to the attacker. Although a checkbox “check here if you are not a bot” might serve to distinguish between humans and computers, it is not a CAPTCHA because it relies on the fact that an attacker has not spent effort to break that specific form.
Some researchers promote image recognition CAPTCHAs as a possible alternative for text based CAPTCHAs. To date, no major website has made use of an image based CAPTCHA. However, many amateur users of the phpBB forum software (which has suffered greatly from spam) have implemented an open source image recognition CAPTCHA system in the form of an addon called KittenAuth which in its default form presents a question requiring the user to select a stated type of animal from an array of thumbnail images of assorted animals. The images (and the challenge questions) can be customized, for example to present questions and images which would be easily answered by the forum’s target userbase.